Assessment and analysis of the demand for groundwater by growers on the Heretaunga Plains, Hawke's Bay

Abstract

This project focuses on issues regarding the extraction of groundwater for horticultural irrigation on the Heretaunga Plains, Hawke's Bay. The Resource Management Act (1991) requires the Hawke's Bay Regional Council to ensure sustainable use of the Heretaunga Plains aquifer. From analysis of the aquifer's water level data, the study found that sustainable use of the resource is not yet an issue. However, there may be limits to extraction in the future as a result of both extreme meteorological conditions and increased demand. The volume of groundwater extracted for irrigation during the 1994-95 season was determined to be ca. 24.7 million m3 using soil, land-use, and survey data, (compared to ca. 23.9 million m3 for the same period calculated by the Hawke's Bay Regional Council). This was an extreme irrigation season because of a prolonged dry spell. Growers from the area were surveyed on their perceptions of the water resource and related management issues. Their main concerns were irrigation efficiency, metering of water usage, chemical use, and their working relationship with the Hawke's Bay Regional Council. Soil-moisture was monitored by Time-Domain Reflectometry for two common forms of orchard irrigation system. This indicated that over-watering is not occurring. This study suggests that policies encouraging monitoring and irrigation efficiency would be more effective in promoting the sustainable use of groundwater than punitive regulations, which would also prove difficult to enforce.